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<a name="glib-Type-Conversion-Macros"></a><div class="titlepage"></div>
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<h2><span class="refentrytitle"><a name="glib-Type-Conversion-Macros.top_of_page"></a>Type Conversion Macros</span></h2>
<p>Type Conversion Macros — portably storing integers in pointer variables</p>
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</tr></table></div>
<div class="refsect1">
<a name="glib-Type-Conversion-Macros.functions"></a><h2>Functions</h2>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="functions_return">
<col class="functions_name">
</colgroup>
<tbody>
<tr>
<td class="define_keyword">#define</td>
<td class="function_name">
<a class="link" href="glib-Type-Conversion-Macros.html#GINT-TO-POINTER:CAPS" title="GINT_TO_POINTER()">GINT_TO_POINTER</a><span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="define_keyword">#define</td>
<td class="function_name">
<a class="link" href="glib-Type-Conversion-Macros.html#GPOINTER-TO-INT:CAPS" title="GPOINTER_TO_INT()">GPOINTER_TO_INT</a><span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="define_keyword">#define</td>
<td class="function_name">
<a class="link" href="glib-Type-Conversion-Macros.html#GUINT-TO-POINTER:CAPS" title="GUINT_TO_POINTER()">GUINT_TO_POINTER</a><span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="define_keyword">#define</td>
<td class="function_name">
<a class="link" href="glib-Type-Conversion-Macros.html#GPOINTER-TO-UINT:CAPS" title="GPOINTER_TO_UINT()">GPOINTER_TO_UINT</a><span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="define_keyword">#define</td>
<td class="function_name">
<a class="link" href="glib-Type-Conversion-Macros.html#GSIZE-TO-POINTER:CAPS" title="GSIZE_TO_POINTER()">GSIZE_TO_POINTER</a><span class="c_punctuation">()</span>
</td>
</tr>
<tr>
<td class="define_keyword">#define</td>
<td class="function_name">
<a class="link" href="glib-Type-Conversion-Macros.html#GPOINTER-TO-SIZE:CAPS" title="GPOINTER_TO_SIZE()">GPOINTER_TO_SIZE</a><span class="c_punctuation">()</span>
</td>
</tr>
</tbody>
</table></div>
</div>
<div class="refsect1">
<a name="glib-Type-Conversion-Macros.includes"></a><h2>Includes</h2>
<pre class="synopsis">#include &lt;glib.h&gt;
</pre>
</div>
<div class="refsect1">
<a name="glib-Type-Conversion-Macros.description"></a><h2>Description</h2>
<p>Many times GLib, GTK+, and other libraries allow you to pass "user
data" to a callback, in the form of a void pointer. From time to time
you want to pass an integer instead of a pointer. You could allocate
an integer, with something like:</p>
<div class="informalexample">
  <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
    <tbody>
      <tr>
        <td class="listing_lines" align="right"><pre>1
2</pre></td>
        <td class="listing_code"><pre class="programlisting"><span class="gtkdoc kwb">int</span> <span class="gtkdoc opt">*</span>ip <span class="gtkdoc opt">=</span> <span class="function"><a href="glib-Memory-Allocation.html#g-new">g_new</a></span> <span class="gtkdoc opt">(</span><span class="gtkdoc kwb">int</span><span class="gtkdoc opt">,</span> <span class="number">1</span><span class="gtkdoc opt">);</span>
<span class="gtkdoc opt">*</span>ip <span class="gtkdoc opt">=</span> <span class="number">42</span><span class="gtkdoc opt">;</span></pre></td>
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    </tbody>
  </table>
</div>

<p>
But this is inconvenient, and it's annoying to have to free the
memory at some later time.</p>
<p>Pointers are always at least 32 bits in size (on all platforms GLib
intends to support). Thus you can store at least 32-bit integer values
in a pointer value. Naively, you might try this, but it's incorrect:</p>
<div class="informalexample">
  <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
    <tbody>
      <tr>
        <td class="listing_lines" align="right"><pre>1
2
3
4</pre></td>
        <td class="listing_code"><pre class="programlisting">gpointer p<span class="gtkdoc opt">;</span>
<span class="gtkdoc kwb">int</span> i<span class="gtkdoc opt">;</span>
p <span class="gtkdoc opt">= (</span><span class="gtkdoc kwb">void</span><span class="gtkdoc opt">*)</span> <span class="number">42</span><span class="gtkdoc opt">;</span>
i <span class="gtkdoc opt">= (</span><span class="gtkdoc kwb">int</span><span class="gtkdoc opt">)</span> p<span class="gtkdoc opt">;</span></pre></td>
      </tr>
    </tbody>
  </table>
</div>

<p>
Again, that example was not correct, don't copy it.
The problem is that on some systems you need to do this:</p>
<div class="informalexample">
  <table class="listing_frame" border="0" cellpadding="0" cellspacing="0">
    <tbody>
      <tr>
        <td class="listing_lines" align="right"><pre>1
2
3
4</pre></td>
        <td class="listing_code"><pre class="programlisting">gpointer p<span class="gtkdoc opt">;</span>
<span class="gtkdoc kwb">int</span> i<span class="gtkdoc opt">;</span>
p <span class="gtkdoc opt">= (</span><span class="gtkdoc kwb">void</span><span class="gtkdoc opt">*) (</span><span class="gtkdoc kwb">long</span><span class="gtkdoc opt">)</span> <span class="number">42</span><span class="gtkdoc opt">;</span>
i <span class="gtkdoc opt">= (</span><span class="gtkdoc kwb">int</span><span class="gtkdoc opt">) (</span><span class="gtkdoc kwb">long</span><span class="gtkdoc opt">)</span> p<span class="gtkdoc opt">;</span></pre></td>
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    </tbody>
  </table>
</div>

<p>
The GLib macros <a class="link" href="glib-Type-Conversion-Macros.html#GPOINTER-TO-INT:CAPS" title="GPOINTER_TO_INT()"><code class="function">GPOINTER_TO_INT()</code></a>, <a class="link" href="glib-Type-Conversion-Macros.html#GINT-TO-POINTER:CAPS" title="GINT_TO_POINTER()"><code class="function">GINT_TO_POINTER()</code></a>, etc. take care
to do the right thing on the every platform.</p>
<p>Warning: You may not store pointers in integers. This is not
portable in any way, shape or form. These macros only allow storing
integers in pointers, and only preserve 32 bits of the integer; values
outside the range of a 32-bit integer will be mangled.</p>
</div>
<div class="refsect1">
<a name="glib-Type-Conversion-Macros.functions_details"></a><h2>Functions</h2>
<div class="refsect2">
<a name="GINT-TO-POINTER:CAPS"></a><h3>GINT_TO_POINTER()</h3>
<pre class="programlisting">#define GINT_TO_POINTER(i) ((gpointer) (glong) (i))
</pre>
<p>Stuffs an integer into a pointer type.</p>
<p>Remember, you may not store pointers in integers. This is not portable
in any way, shape or form. These macros only allow storing integers in
pointers, and only preserve 32 bits of the integer; values outside the
range of a 32-bit integer will be mangled.</p>
<div class="refsect3">
<a name="GINT-TO-POINTER.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody><tr>
<td class="parameter_name"><p>i</p></td>
<td class="parameter_description"><p>integer to stuff into a pointer</p></td>
<td class="parameter_annotations"> </td>
</tr></tbody>
</table></div>
</div>
</div>
<hr>
<div class="refsect2">
<a name="GPOINTER-TO-INT:CAPS"></a><h3>GPOINTER_TO_INT()</h3>
<pre class="programlisting">#define GPOINTER_TO_INT(p) ((gint)  (glong) (p))
</pre>
<p>Extracts an integer from a pointer. The integer must have
been stored in the pointer with <a class="link" href="glib-Type-Conversion-Macros.html#GINT-TO-POINTER:CAPS" title="GINT_TO_POINTER()"><code class="function">GINT_TO_POINTER()</code></a>.</p>
<p>Remember, you may not store pointers in integers. This is not portable
in any way, shape or form. These macros only allow storing integers in
pointers, and only preserve 32 bits of the integer; values outside the
range of a 32-bit integer will be mangled.</p>
<div class="refsect3">
<a name="GPOINTER-TO-INT.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody><tr>
<td class="parameter_name"><p>p</p></td>
<td class="parameter_description"><p>pointer containing an integer</p></td>
<td class="parameter_annotations"> </td>
</tr></tbody>
</table></div>
</div>
</div>
<hr>
<div class="refsect2">
<a name="GUINT-TO-POINTER:CAPS"></a><h3>GUINT_TO_POINTER()</h3>
<pre class="programlisting">#define GUINT_TO_POINTER(u) ((gpointer) (gulong) (u))
</pre>
<p>Stuffs an unsigned integer into a pointer type.</p>
<div class="refsect3">
<a name="GUINT-TO-POINTER.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody><tr>
<td class="parameter_name"><p>u</p></td>
<td class="parameter_description"><p>unsigned integer to stuff into the pointer</p></td>
<td class="parameter_annotations"> </td>
</tr></tbody>
</table></div>
</div>
</div>
<hr>
<div class="refsect2">
<a name="GPOINTER-TO-UINT:CAPS"></a><h3>GPOINTER_TO_UINT()</h3>
<pre class="programlisting">#define GPOINTER_TO_UINT(p) ((guint) (gulong) (p))
</pre>
<p>Extracts an unsigned integer from a pointer. The integer must have
been stored in the pointer with <a class="link" href="glib-Type-Conversion-Macros.html#GUINT-TO-POINTER:CAPS" title="GUINT_TO_POINTER()"><code class="function">GUINT_TO_POINTER()</code></a>.</p>
<div class="refsect3">
<a name="GPOINTER-TO-UINT.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody><tr>
<td class="parameter_name"><p>p</p></td>
<td class="parameter_description"><p>pointer to extract an unsigned integer from</p></td>
<td class="parameter_annotations"> </td>
</tr></tbody>
</table></div>
</div>
</div>
<hr>
<div class="refsect2">
<a name="GSIZE-TO-POINTER:CAPS"></a><h3>GSIZE_TO_POINTER()</h3>
<pre class="programlisting">#define GSIZE_TO_POINTER(s) ((gpointer) (gsize) (s))
</pre>
<p>Stuffs a <a class="link" href="glib-Basic-Types.html#gsize" title="gsize"><span class="type">gsize</span></a> into a pointer type.</p>
<div class="refsect3">
<a name="GSIZE-TO-POINTER.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody><tr>
<td class="parameter_name"><p>s</p></td>
<td class="parameter_description"><p><a class="link" href="glib-Basic-Types.html#gsize" title="gsize"><span class="type">gsize</span></a> to stuff into the pointer</p></td>
<td class="parameter_annotations"> </td>
</tr></tbody>
</table></div>
</div>
</div>
<hr>
<div class="refsect2">
<a name="GPOINTER-TO-SIZE:CAPS"></a><h3>GPOINTER_TO_SIZE()</h3>
<pre class="programlisting">#define GPOINTER_TO_SIZE(p) ((gsize) (p))
</pre>
<p>Extracts a <a class="link" href="glib-Basic-Types.html#gsize" title="gsize"><span class="type">gsize</span></a> from a pointer. The <a class="link" href="glib-Basic-Types.html#gsize" title="gsize"><span class="type">gsize</span></a> must have
been stored in the pointer with <a class="link" href="glib-Type-Conversion-Macros.html#GSIZE-TO-POINTER:CAPS" title="GSIZE_TO_POINTER()"><code class="function">GSIZE_TO_POINTER()</code></a>.</p>
<div class="refsect3">
<a name="GPOINTER-TO-SIZE.parameters"></a><h4>Parameters</h4>
<div class="informaltable"><table class="informaltable" width="100%" border="0">
<colgroup>
<col width="150px" class="parameters_name">
<col class="parameters_description">
<col width="200px" class="parameters_annotations">
</colgroup>
<tbody><tr>
<td class="parameter_name"><p>p</p></td>
<td class="parameter_description"><p>pointer to extract a <a class="link" href="glib-Basic-Types.html#gsize" title="gsize"><span class="type">gsize</span></a> from</p></td>
<td class="parameter_annotations"> </td>
</tr></tbody>
</table></div>
</div>
</div>
</div>
<div class="refsect1">
<a name="glib-Type-Conversion-Macros.other_details"></a><h2>Types and Values</h2>
</div>
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